Synergistic rhenium and germanium-containing catalysts potentiated with tin and alkylaromatic transalkylation processes using such catalysts

ABSTRACT

Transalkylation catalysts comprising acidic molecular sieve, rhenium, tin and germanium have good activities and attenuate aromatic ring saturation and lights co-production.

FIELD OF THE INVENTION

This invention relates to improved catalysts and processes fortransalkylation of alkylaromatics. The catalysts contain rhenium andcertain amounts of germanium and tin to provide low ring loss yetachieve desirable conversions with attractive catalyst selectivities.

BACKGROUND OF THE INVENTION

The xylene isomers are produced in large volumes from petroleum asfeedstocks for a variety of important industrial chemicals. The mostimportant of the xylene isomers is para-xylene, the principal feedstockfor polyester, which continues to enjoy a high growth rate from largebase demand. Ortho-xylene is used to produce phthalic anhydride, whichsupplies high-volume but relatively mature markets. Meta-xylene is usedin lesser but growing volumes for such products as plasticizers, azodyes and wood preservers.

A prior art aromatics complex flow scheme has been disclosed by Meyersin part 2 of the Handbook of Petroleum Refining Processes, 2d. Edition,in 1997 published by McGraw-Hill.

In general, a xylene production facility can have various types ofprocessing reactions. One is a transalkylation in which benzene and/ortoluene are reacted with C₉+ aromatics to form more methylatedaromatics. Another is xylene isomerization, which may also includedealkylation, where a non-equilibrium mixture of xylenes is isomerized.And another is the disproportionation of toluene to yield one mole ofbenzene per mole of xylene produced.

In the transalkylation process, adverse side reactions can occur. Forinstance, the aromatic ring may become saturated or even cleavedresulting in naphthene co-production. The co-production of thesenon-aromatics, of course, results in a loss of valuable aromatics.Moreover, benzene is often a sought co-product from a xylene productionfacility. As some of the naphthenes have similar boiling points tobenzene, they are not readily removed to achieve a benzene product ofsought purity for commercial applications which frequently demand abenzene product having at least a 99.85 percent purity.

Accordingly, a need exists for catalysts and processes for thetransalkylation of alkylaromatics, which processes have desirableselectivity of conversion to the desired alkylaromatics such as xylenes,yet at sufficiently high rates of conversion to be commerciallyfeasible.

U.S. Pat. No. 3,562,345 (Mitsche) discloses catalysts fortransalkylation or disproportionation of alkylaromatics comprising analuminosilicates such as mordenite. Catalytically active metals such asgroups VIB and VIII metals may be present.

U.S. Pat. No. 3,951,868 (Wilhelm) discloses catalysts for hydrocarbonconversions comprising a platinum group metal and indium with optionallya Group IVA component such as germanium or tin.

U.S. Pat. No. 4,331,822 (Onodera, et al.) discloses catalysts for xyleneisomerization containing molecular sieve such as ZSM-5, platinum and atleast one metal from the group of titanium, chromium, zinc, gallium,germanium, strontium, yttrium, zirconium, molybdenum, palladium, tin,barium, cesium, cerium, tungsten, osmium, lead, cadmium, mercury,indium, lanthanum, beryllium, lithium and rubidium.

U.S. Pat. No. 5,847,256 (Ichioka et al.) discloses a process forproducing xylene from a feedstock containing C₉ alkylaromatics withethyl-groups over a catalyst containing a zeolite component that ispreferably mordenite and with a metal component that is preferablyrhenium.

U.S. Pat. No. 6,060,417 (Kato, et al.) discloses catalysts and processesfor transalkylation of alkylaromatics wherein the catalysts comprisemordenite, inorganic oxide and/or clay and at least one metal componentof rhenium, platinum and nickel. See also, U.S. Pat. No. 6,359,184(Kato, et al.).

U.S. Pats. Nos. 6,150,292 and 6,465,705 (Merlen, et al.) disclose axylene isomerization process using a mordenite-containing catalyst thatfurther contains at least one platinum group metal and at least onemetal from group III of the periodic table such as gallium, indium orthallium and optionally at least one metal from group IV of the periodictable such as germanium, tin or lead.

U.S. Pats. Nos. 6,613,709 and 6,864,400 (Merlen, et al.) disclose atransalkylation catalyst containing zeolite NES and at lease one metalselected from group VIIB, group VIB and iridium with optionally at leastone metal selected from groups III and IV of the periodic table,preferably indium and tin.

U.S. Pat. No. 6,855,854 (James, Jr.) discloses a process using twotransalkylation catalysts to react C₉+ aromatics with benzene. Thecatalyst comprises zeolite and optional metal components such as IUPAC8-10 metal and modifier such as tin, germanium, lead, indium, andmixtures thereof.

U.S. Pat. No. 6,872,866 (Nemeth, et al.) discloses a liquid phase xyleneisomerization process which uses a zeolite beta and pentasil-typezeolite. The catalyst can contain a hydrogenation metal component suchas a platinum group metal and modifiers such as rhenium, tin, germanium,lead, cobalt, nickel, indium, gallium, zinc, uranium, dysprosium,thallium, and mixtures thereof.

SUMMARY OF THE INVENTION

In accordance with this invention, rhenium-containing catalysts areprovided that exhibit desirable transalkylation activities andselectivities with relatively low co-production of lights andnon-aromatic benzene coboilers. As used herein, the term transalkylationis intended to include transalkylation between and among alkylaromaticsas well as between benzene and alkylaromatics. By this invention, it hasbeen found that in the presence of a combination of tin and geranium inrespect to the rhenium, adverse ring saturation, ring cleavage, andlights co-production can be substantially attenuated.

In one broad aspect, the catalysts of this invention comprise acatalytically effective amount of acidic molecular sieve, at least about0.05, and more preferably between about 0.1 and 1, most preferablybetween about 0.15 and 1, mass percent rhenium calculated on anelemental basis, and a combination of tin and germanium where thecatalyst, under Evaluation Conditions, exhibits a lower Ring Loss thanan essentially identical catalyst but not containing tin and than anessentially identical catalyst but not containing germanium.

Evaluation Conditions are:

Feedstock (+/−0.5%-mass): Toluene: 75%-mass Trimethylbenzene: 10%-massMethylethylbenzene: 10%-mass Propylbenzene: 2%-massDimethylethylbenzene: 1%-mass Diethylbenzene: 0.5%-massTetramethylbenzene: 0.5%-mass Other alkylaromatics balance and benzene:Pressure: 1725 kPa (absolute) WHSV, hr⁻¹: 4 H₂:HC: 6 Overall Conversion:30%-mass

Ring Loss is determined as the difference between the mass of totalaromatics in the feed to the transalkylation reactor and the mass oftotal aromatics in the effluent from the alkylation reactor expressed inmass percent. H₂:HC is the hydrogen to hydrocarbon mole ratio. Overallconversion is the weighted average conversion of the compounds in thefeed.

Often the atomic ratio of germanium to rhenium is at least about 2:1,say, about 2:1 to 50:1, and preferably between about 2.5:1 to 25:1. Theamount of tin can vary widely and is often in an atomic ratio to rheniumof at least about 0.1:1, preferably at least about 0.2:1, say, about 0.2to 20:1.

Another aspect of the transalkylation catalysts of this inventioncomprises a catalytically effective amount of acidic molecular sieve, acatalytically effective amount of rhenium said amount being at leastabout 0.05, and more preferably between about 0.1 and 1, most preferablybetween about 0.15 and 1, mass percent rhenium calculated on anelemental basis, and a combination of tin and germanium wherein theatomic ratio of germanium to rhenium is at least about 2:1 and theatomic ratio of tin to rhenium is at least about 0.1:1.

One broad aspect of the transalkylation processes of this inventioncomprises subjecting a transalkylation feed stream comprising lighteraromatics and heavier aromatics to transalkylation conditions includingthe presence of transalkylation catalyst comprising at least about 0.05,and more preferably between about 0.1 and 1, most preferably betweenabout 0.15 and 1, mass percent rhenium calculated on an elemental basis,and a combination of tin and germanium where the process achieves alower Ring Loss than an substantially identical transalkylation processbut using an essentially identical catalyst but not containing tin andthan an substantially identical transalkylation process but using anessentially identical catalyst but not containing germanium.

In another aspect, the transalkylation processes of this inventioncomprise subjecting a transalkylation feed stream comprising lighteraromatics and heavier aromatics to transalkylation conditions includingthe presence of transalkylation catalyst comprising a catalyticallyeffective amount of acidic molecular sieve, a catalytically effectiveamount of rhenium said amount at least about 0.05, and more preferablybetween about 0.1 and 1, most preferably between about 0.15 and 1, masspercent rhenium calculated on an elemental basis, and a combination oftin and germanium wherein the atomic ratio of germanium to rhenium is atleast about 2:1 and the atomic ratio of tin to rhenium is at least about0.1:1.

DETAILED DESCRIPTION OF THE INVENTION

The Process

The processes of this invention comprise transalkylation between lighter(non- or less substituted) aromatics and heavier, greater substitutedalkylaromatics with the product being alkylaromatics having the numberof substitutions between those of the lighter fraction and those of theheavier fraction. The lighter aromatics have 0 to 2 substitutions andthe heavier aromatics have 2 to 5 substitutions with the product fallingin between. For example, benzene may be transalkylated withmethylethylbenzene to provide toluene and ethylbenzene. Similarly,benzene or toluene may be transalkylated with trimethylbenzene toprovide xylene. In some instances for xylene production facilities, itmay be desired to consume benzene in the transalkylation rather thanproducing it as a co-product in which case benzene may comprise from 5to 80, preferably 10 to 60, mass percent of the lighter aromatics.

Thus the feedstream to the present process generally comprisesalkylaromatic hydrocarbons of the general formula C₆H_((6-n))R_(n),where n is an integer from 0 to 5 and each R may be CH₃, C₂H₅, C₃H₇, orC₄H₉, in any combination. Suitable alkylaromatic hydrocarbons include,for example but without so limiting the invention, benzene, toluene,ortho-xylene, meta-xylene, para-xylene, ethylbenzene, ethyltoluenes,propylbenzenes, tetramethylbenzenes, ethyl-dimethylbenzenes,diethylbenzenes, methylpropylbenzenes, ethylpropylbenzenes,triethylbenzenes, di-isopropylbenzenes, and mixtures thereof.

Where the sought product is xylenes or ethylbenzene, the feed streampreferably comprises as the lighter fraction, at least one of benzeneand toluene and as the heavier fraction, at least one C₉+ aromaticcompounds. The molar ratio of benzene and toluene to C₉+ aromatics ispreferably from about 0.3:1 to about 10:1 and even more preferably fromabout 0.4:1 to about 6:1. A preferred component of the feedstock wherethe sought product is xylenes is a heavy-aromatics stream comprising C₉+aromatics. C₁₀+ aromatics also may be present, typically in an amount of50 wt-% or less of the feed. The heavy-aromatics stream generallycomprises at least about 90 wt-% aromatics.

The feedstock is preferably transalkylated in the gas-phase and in thepresence of hydrogen. If the feedstock is transalkylated in thegas-phase, then hydrogen is added, commonly in an amount of from about0.1 moles per mole of alkylaromatics up to 10 moles per mole of totalaromatic compounds in the feed. This ratio of hydrogen to aromaticcompound is also referred to as hydrogen to hydrocarbon ratio. If thetransalkylation is conducted in the liquid phase, it is usually done ina substantial absence of hydrogen beyond what may already be present anddissolved in a typical liquid aromatics feedstock. In the case ofpartial liquid phase, hydrogen may be added in an amount less than 1mole per mole of alkylaromatics.

Transalkylation conditions typically comprise elevated temperature,e.g., from about 100° C. to about 540° C., preferably, from about 200°C. to about 500° C. Often, in commercial facilities, the transalkylationtemperature is increased to compensate with any decreasing activity ofthe catalyst. The feed to a transalkylation reaction zone usually firstis heated by indirect heat exchange against the effluent of the reactionzone and then is heated to reaction temperature by exchange with awarmer stream, steam or a furnace. The feed then is passed through areaction zone, which may comprise one or more individual reactorscontaining catalyst of this invention.

The reactors may be of any suitable type and configuration. The use of asingle reaction vessel having a fixed cylindrical bed of catalyst ispreferred, but other reaction configurations utilizing moving beds ofcatalyst or radial-flow reactors may be employed if desired.

Transalkylation conditions include pressures ranging from about 100 kPato about 6 MPa absolute, preferably from about 0.5 to about 5 MPaabsolute. The transalkylation reaction can be effected over a wide rangeof space velocities. The weight hourly space velocity (WHSV) generallyis in the range of from about 0.1 to about 20 hr⁻¹ preferably from about0.5 to about 15 hr⁻¹, and most often between about 1 to about 5 hr⁻¹.

Advantageously, the transalkylation is conducted for a time and underother conditions sufficient that at least about 10, preferably at leastabout 20, and often between about 20 and 45, mole percent of the heavieralkylaromatic is consumed. Preferably, of the heavier alkylaromaticsconsumed, at least about 70, most preferably at least about 75, molepercent are converted to lower molecular weight aromatics. The preferredtransalkylation products are xylenes for a xylene production facility.

The effluent from the transalkylation typically contains, in addition tothe transalkylation product, unreacted lighter and heavier aromatics.Co-products such as naphthenes and lights will also be present.Typically this effluent is normally cooled by indirect heat exchangeagainst the feed to the reaction zone and then further cooled throughthe use of air or cooling water. The effluent may be subjected todistillation in which substantially all C₅ and lighter hydrocarbonspresent in the effluent are provided in an overhead stream and removedfrom the process. In the same or a different distillation, at least aportion of the unreacted lights are recovered for recycle. Atransalkylation product fraction can be withdrawn, and a heavies streamprovided. All or a portion of the heavies stream may be recycled to thetransalkylation zone. All or a portion of the lighter aromatics can berecycled to the transalkylation zone.

The Catalyst

The catalysts of this invention comprise acidic molecular sieve,rhenium, tin and germanium. Molecular sieves include, but are notlimited to, zeolite beta, zeolite MTW, zeolite Y (both cubic andhexagonal forms), zeolite X, mordenite, zeolite L, zeolite ferrierite,MFI, and erionite. Zeolite beta is described in U.S. Pat. No. 3,308,069according to its structure, composition, and preferred methods ofsynthesis. Y zeolites are broadly defined in U.S. Pat. No. 3,130,007,which also includes synthesis and structural details. Mordenite is anaturally occurring siliceous zeolite which can have molecular channelsdefined by either 8 or 12 member rings. Donald W. Breck describes thestructure and properties of mordenite in Zeolite Molecular Sieves (JohnWiley and Sons, 1974, pp. 122-124 and 162-163). Zeolite L is defined inU.S. Pat. No. 3,216,789, which also provides information on its uniquestructure as well as its synthesis details. Other examples of zeolitesthat can be used are those having known structure types, as classifiedaccording to their three-letter designation by the Structure Commissionof the International Zeolite Association (“Atlas of Zeolite StructureTypes”, by Meier, W. M.; Olsen, D. H; and Baerlocher, Ch., 1996) of MFI,FER, ERI, MTW and FAU. Zeolite X is a specific example of the latterstructure type. The preferred molecular sieves are acidic molecularsieves having a pore size of at least about 6 Angstroms, say 6 to 12,Angstroms. Mordenite is one specific type of preferred molecular sieves.The molecular sieves useful in this invention include those that aretreated after synthesis, e.g., by dealumination, exchange, andcalcination.

A refractory binder or matrix is optionally utilized to facilitatefabrication of the catalyst, provide strength and reduce fabricationcosts. The binder should be uniform in composition and relativelyrefractory to the conditions used in the process. Suitable bindersinclude inorganic oxides such as one or more of alumina, magnesia,zirconia, chromia, titania, boria, thoria, phosphate, zinc oxide andsilica.

The molecular sieve may be present in a range from 5 to 99 mass percentof the catalyst and the refractory inorganic oxide may be present in arange of from about 1 to 95 mass percent. Alumina is an especiallypreferred inorganic oxide binder.

The catalyst also contains rhenium. Rhenium may exist within the finalcatalytic composite as a compound such as an oxide or sulfide or inchemical combination with one or more of the other ingredients of thecomposite, or, preferably, as an elemental metal. This component may bepresent in the final catalyst composite in any amount which iscatalytically effective, generally comprising at least about 0.05, andmore preferably between about 0.1 and 1, mass percent of the finalcatalyst calculated on an elemental basis. The rhenium component may beincorporated into the catalyst in any suitable manner such as comulling,coprecipitation or cogelation with the carrier material, ion exchange orimpregnation.

The catalyst also contains germanium and tin. The optimum relativeamounts of rhenium and germanium will vary depending upon, for instance,the amount of rhenium provided on the catalyst. All combinations ofrhenium, tin and germanium do not provide a better performing catalystthan one just containing rhenium and tin or just containing rhenium andgermanium as the metal components. In general, too much germanium tendsto depress the activity of the catalyst.

The most advantageous catalysts of this invention exhibit a synergisticperformance, i.e., a lower Ring Loss is exhibited than with anessentially identical process but using a catalyst not having the tin ora catalyst not having the germanium component. One means for determiningwhether the catalyst possesses synergism is to conduct an evaluationunder Evaluation Conditions, even though those transalkylationconditions may be different than those for the intended use of thecatalyst. In a commercial facility, it is impractical not only tospecially make the comparative catalysts but also to have down time forcatalyst turn-around and to operate the facility in less than a mostproductive fashion when using comparative catalysts. Accordingly, pilotscale tests at the temperature, pressure and weight hourly spacevelocity used in the commercial facility can be used for determiningwhether the catalyst exhibits a synergistic effect for thecommercially-practice process.

The germanium and tin components may be incorporated into the catalystin any suitable manner such as comulling, coprecipitation or cogelationwith the carrier material, ion exchange or impregnation. Frequently,water or alcohol soluble compounds of the metal are used for theimpregnation. The incorporation of each of tin and germanium into thecatalyst may precede, follow or be simultaneous with the incorporationof the rhenium component.

The catalyst may optionally contain an additional modifier component.Preferred additional metal modifier components of the catalyst include,for example, lead, indium, and mixtures thereof. Catalytically effectiveamounts of such metal modifiers may be incorporated into the catalyst byany suitable manner. A preferred amount is a range of about 0.01 toabout 2.0 mass percent on an elemental basis.

Generally, water may have a deleterious effect on the catalyst andprolonged contact with the catalyst will cause a loss of activity asdescribed in U.S. Pat. No. 5,177,285 and U.S. Pat. No. 5,030,786. Thus,a typically low water concentration of less than about 200 wt-ppmresults in reasonable operation.

EXAMPLES

In the following examples, all parts and percentages of liquids andsolids are by mass and those of gases are molar, unless otherwise statedor apparent from the context. The following examples are illustrativeonly and are not in limitation of the broad aspects of the invention.

Example 1

A series of supported catalysts are prepared using the followingprocedure. An impregnating solution containing appropriate amounts ofmetal components to provide the desired metal content in the finalcatalyst is added to the container. Each impregnating solution is madeusing appropriate amounts of one or more of the following stock reagentsto provide the sought metal content on the catalyst:Perrhenic acid (HReO₄) in water, 1.07%-mass ReTin (IV) Chloride (SnCl₄) in water, 2.7%-mass SnGermanium ethoxide (Ge(OCH₂CH₃)₄) in 1-propanol, 0.75%-mass Ge.

The tin chloride solution is believed to be unstable, and tin canprecipitate and not be provided on the catalyst. Moreover, tin maydeposit on the walls of the container as opposed to the catalystparticles. The alternative deposition of tin is believed to be relatedto how fresh the impregnating solution is. Hence, it is highly likelythat the amount of tin in the catalysts is less than that targeted andthat the amount of tin deposited on the catalyst is unpredictable.

Distilled water is added to each impregnating solution to provide about7.4 milliliters of impregnating solution per gram of support. Amordenite support material containing 75 weight parts mordenite (H-MOR)and 25 weight parts gamma alumina as binder is placed in the container.The mordenite has a silica to alumina ratio of about 20:1. The particlesize of the support is that sieved to the range of about 0.25 to 0.43millimeter. The mixture is dried in a rotary evaporator untilfree-flowing. The impregnated catalyst is then dried in air at about100° C. for about one hour and calcined in air at about 510° C. forabout 6 hours.

The catalysts are evaluated for transalkylation properties with afeedstock comprising 50 mole percent toluene, 25 mole percent1,3,5-trimethylbenzene, and 25 mole percent 4-ethyltoluene. Theevaluation is conducted under a pressure of about 2800 kPa absolute, aweight hourly space velocity of about 3 hr⁻¹ and the conditions setforth in Table I. The performance results are also provided in Table I.

TABLE I Targeted MEB Xylene C6 + NA Metal, %-mass Conversion SelectivityMake Catalyst Temp, ° C. H₂:HC Re Sn¹ Ge Mole-% Mole-% Mole-% A* 0.5 0.00.0 72 62 7 B* 0.5 0.3 0.0 83 65 2 C* 0.5 0.0 0.3 72 68 4 D* 0.5 0.3 0.372 63 6 E 0.5 0.3 0.5 75 70 4 F* 0.5 0.5 0.0 83 63 2 G* 0.5 0.0 0.5 7568 4 H* 0.5 0.5 0.3 87 67 2 I 0.5 0.5 0.5 80 66 1 J* 0.3 0.0 0.0 72 64 5K* 0.3 0.3 0.0 82 66 1 L* 0.3 0.0 0.3 81 63 5 M 0.3 0.3 0.3 68 70 0.9 N0.3 0.3 0.5 83 66 1 O* 0.3 0.5 0.0 83 68 1.5 P* 0.3 0.0 0.5 82 66 3 Q0.3 0.5 0.3 80 67 0.8 R 0.3 0.5 0.5 70 68 1.2 S* 0.1 0.0 0.0 78 66 2 T*0.1 0.3 0.0 76 67 1.2 U* 0.1 0.0 0.3 77 68 1 V 0.1 0.3 0.3 76 67 1.5 W0.1 0.3 0.5 76 68 0.8 X* 0.1 0.5 0.0 83 68 1.8 Y* 0.1 0.0 0.5 80 67 2 Z0.1 0.5 0.3 80 67 1.2 AA 0.1 0.5 0.5 62 74 0.7 *comparative ¹actualamount of tin is expected to be less and unpredictable

The data in Table I are not conclusive due to the variation in tin.However, they do indicate that a potential interaction among rhenium,tin and germanium may exist. Accordingly, additional catalysts withmeasured tin content are made and tested.

Example 2

Another series of supported catalysts are prepared using the followingprocedure. An impregnating solution containing appropriate amounts ofmetal components to provide the desired metal content in the finalcatalyst is added to the container. Each impregnating solution is madeusing appropriate amounts of one or more of the following stock reagentsto provide the sought metal content on the catalyst:Perrhenic acid (HReO₄) in water, 1.07%-mass ReTin (IV) Chloride (SnCl₄) in water, 2.7%-mass SnGermanium ethoxide (Ge(OCH₂CH₃)₄) in 1-propanol, 0.75%-mass Ge

Distilled water is added to each impregnating solution to provide aboutan equal volume to the volume of the support. A mordenite supportmaterial containing 75 weight parts mordenite (H-MOR) and 25 weightparts gamma alumina as binder is placed in the container. The mordenitehas a silica to alumina ratio of about 20:1. The support is cylindricalpellet having a diameter of about 1.6 millimeters and a length todiameter ratio of about 4. The mixture is dried in a rotary evaporatorby cold rolling until free-flowing. The impregnated catalyst is thendried in air at about 100° C. for about one hour and calcined in air atabout 510° C. for about 6 hours.

Table II describes the catalysts. The amounts of rhenium, tin andgermanium are determined by ICP analysis.

TABLE II Re, % Sn, %- Ge, %- CATALYST mass mass mass L-1 (COMP) 0.29 00.32 L-2 (COMP) 0.29 0.11 0.0 L-3 0.28 0.075 0.29 L-4 0.27 0.1 0.27

Example 3

The catalysts prepared in Example 2 are evaluated for transalkylationactivity. The feed contains:

Toluene: 74.7%-mass  Trimethylbenzene: 9.6%-mass Methylethylbenzene:9.9%-mass Diethylbenzene 0.4%-mass Dimethylethylbenzene 1.1%-mass Otherbalance

The weight hourly space velocity is about 4 hr⁻¹, pressure is about 1725kPa (gauge), and hydrogen is provided in an amount to provide a hydrogento hydrocarbon ratio of about 5.8:1.

The results of the evaluation are summarized in Table III.

TABLE III Performance Overall MEB Aromatic Ring TEMP, Conversionconversion Loss CATALYST ° C. %-mass %-mass %-mass L-1* 338 26.3 39.70.67 349 32.4 51.8 0.91 362 38.0 63.5 1.21 372 42.5 73.2 1.53 L-2* 33826.2 36.7 1.24 349 31.5 46.6 1.41 362 36.2 56.7 1.62 372 39.8 65.3 1.85L-3 338 24.0 35.3 0.50 349 29.6 40.6 0.67 362 35.5 57.1 0.89 372 40.067.1 1.22 L-4 338 24.0 35.3 0.50 349 29.6 40.6 0.67 362 35.5 57.9 0.89372 40.4 68.4 1.22 *comparative

The data summarized in Table III illustrate that the addition of tin toa rhenium and germanium-containing catalyst reduces Aromatic Ring Loss.A tin and rhenium-containing catalyst exhibits a greater Ring Loss thanthat of a germanium and rhenium-containing catalyst.

1. A catalyst suitable for the transalkylation of alkylaromaticcompounds comprising a catalytically effective amount of acidicmolecular sieve, at least about 0.05 mass percent rhenium calculated onan elemental basis, and a combination of tin and germanium where thecatalyst, under Evaluation Conditions, exhibits a lower Ring Loss thanan essentially identical catalyst but not containing tin and than anessentially identical catalyst but not containing germanium.
 2. Thecatalyst of claim 1 in which the acidic molecular sieve comprisesmordenite.
 3. The catalyst of claim 2 in which the atomic ratio ofgermanium to rhenium is at least about 2:1 and the atomic ratio of tinto rhenium is at least about 0.1:1.
 4. A catalyst suitable for thetransalkylation of alkylaromatic compounds comprising a catalyticallyeffective amount of acidic molecular sieve, a catalytically effectiveamount of rhenium and a combination of tin and germanium wherein theatomic ratio of total tin and germanium to rhenium is at least about 3:1and the atomic ratio of tin to germanium is at least about 0.2:1.
 5. Thecatalyst of claim 4 in which the acidic molecular sieve comprisesmolecular sieve having a pore size of at least about 6 Angstroms.
 6. Thecatalyst of claim 5 in which the acidic molecular sieve comprisesmordenite.
 7. The catalyst of claim 6 in which the rhenium is in anamount of between about 0.1 and 1 mass percent calculated on anelemental basis.
 8. The catalyst of claim 7 in which the atomic ratio ofgermanium to rhenium is about 2:1 to 50:1, and the atomic ratio of tinto germanium is in the range of about 0.2:1 to 20:1.
 9. The catalyst ofclaim 8 comprising a binder, and mordenite is in an amount of betweenabout 5 to 95 mass percent based upon the mass of the catalyst.